1. Field of the Invention
The present invention relates to a magnetic recording medium, a magnetic recording playback device, and an information processing device.
2. Description of the Related Art
With respect to the information processing technology of magnetic disk devices and the like, a large increase in capacity is required with remarkable increases in the amount of information processing in recent years. In particular, the amount of recording information of hard disk per unit area is now on a pace to increase at an annual rate exceeding 60 percent. A future increase in the amount of recording information is also desired, and miniaturization and an increase in density are also required of portable and other recording devices.
Magnetic recording media previously used for hard disks are of longitudinal magnetic recording type, and the magnetization is recorded parallel to a disk surface. In this longitudinal magnetic recording type, demagnetization in the magnetic domain must be suppressed with an increase in density, and a magnetic recording layer must be thinned in order to generate a magnetic field above the medium for the purpose of detecting the magnetization state. Consequently, the volume per magnetic fine particle becomes extremely small, and the superparamagnetic effect becomes remarkable. That is, the energy for stabilizing the magnetization direction becomes smaller than the thermal energy, the recorded magnetization varies with time and, thereby, the record may be deleted. Therefore, in recent years, researches have been actively conducted on the shift from the longitudinal magnetic recording type to the perpendicular magnetic recording type capable of increasing the film thickness of the recording layer.
With respect to a medium for the perpendicular magnetic recording, as shown in FIG. 4A, a Co—Cr alloy is generally used as a recording layer 44, and when prepared by a sputtering method, as shown in FIG. 4B, the recording layer 44 grows while being separated into core portions 46 having a large Co content and shell portions 47 having a relatively large Cr content and surrounding the core portions. The core portion 46 is nearly in the shape of a circular cylinder, exhibits hard magnetism with a hexagonal close-packed lattice structure (hereafter referred to as an hcp structure), and becomes a recording portion. The shell portion 47 has a large Cr content, has a soft magnetic or non-magnetic property, and serves the function of weakening the interaction between adjacent core portions as well. In the core portion 46, the c axis points in the direction perpendicular to the substrate surface, and the magnetization points in the direction perpendicular to the substrate surface due to the action of the magnetocrystalline anisotropy. Besides Co—Cr, for example, Ta, Pt, Rh, Pd, Ti, Nb and Hf are added to the above-described recording layer 44.
However, with respect to further increase in the recording density in the future, it is predicted that reduction in the size of the core portion 46 of the Co—Cr system will be difficult. Since the superparamagnetism effect becomes remarkable with reduction in the size, recently noted L10 ordered alloys of CoPt, FePt, and FePd are believed to be promising materials in the future. In particular, for example, Japanese Patent Laid-Open No. 2001-273622 proposes a medium capable of resisting the superparamagnetism effect accompanying the reduction in the size of magnetic particles of Co—Cr system, wherein the above-described ordered alloy is made into fine particles, and a film (granular film) is prepared, in which the resulting fine particles are dispersed in a non-magnetic matrix. However, it is important to control the volume distribution of the magnetic materials made into fine particles.
The patterned media is a noteworthy media after the perpendicular magnetic recording. The patterned media is a recording system included in the perpendicular recording. However, in contrast to that described above, information is recorded by the orientation of the magnetization of each magnetic material portion. The magnetic materials are required to have a regular arrangement with some periodicity, and an increase in area is a significant challenge because the preparation is difficult.
With respect to the above-described perpendicular magnetic recording media and the patterned media, there is a problem of variations in the sizes of magnetic materials of each medium regardless of difference in the sizes of magnetic materials between the media.